Natural Gamma-Ray Background Characterization in Pyhasalmi Mine

<p>We present the results of measuring the gamma-ray background performance of Pyhasalmi mine, the deepest one in Europe. Two underground facilities in Lab 2 (1440 m) and Lab 5 (1410 m) were investigated. Based on measurements made in Lab 2 with a low-background HPGe spectrometer, we determined the integral gamma-ray background count rate in the energy range of 40 keV to 2.7 MeV to be 0.095 s<sup>–1</sup> kg<sup>–1</sup>. The minimum detectable activities of some natural and artificial nuclides were less than 0.071 Bq/kg (<sup>226</sup>Ra), 0.77 Bq/kg (<sup>40</sup>K) and 0.012 Bq/kg (<sup>137</sup>Cs). The specific activities of natural nuclides in the shotcrete covering the walls of the Lab 2 were higher than those in the rock: 100.3 Bq/kg (<sup>232</sup>Th), 161.7 Bq/kg (<sup>226</sup>Ra) and 1171 Bq/kg (<sup>40</sup>K) in the shotcrete covering and 47.6 Bq/kg (<sup>232</sup>Th), 83.1 Bq/kg (<sup>226</sup>Ra) and 1513 Bq/kg (<sup>40</sup>K) in the rock. The measurements showed that the gamma-ray background level in Lab 5 is significantly lower than that in Lab 2. The integrated gamma-ray background count rate for the energy range of 40 keV to 2.7 MeV was 0.028 s<sup>–1</sup> kg<sup>–1</sup> for Lab 5. Purging the measuring chamber of the gamma spectrometer with nitrogen gas at a rate of 0.15 L/h allowed to further improve this parameter to 0.021 s<sup>–1</sup> kg<sup>–1</sup>. In general, the results of this study confirm that the level and energy spectrum of background gamma radiation in the underground facility within the studied energy range is defined mainly by the composition of the walls of the Labs.</p><p> </p>

Isomer ratios for products of photonuclear reactions on Rh

Over the past several years various preequilibrium models for nuclear reaction mechanisms description were developed. Diversified detailed experimental data in the medium excitation energy region for nuclei are needed for reasonable selection among these theoretical models. Lack of experimental data in this energy region does essentially limit the possibilities for analysis and comparison of different preequilibrium theoretical models. For photonuclear reactions this energy range covers 30-100 MeV. Experimental measurements and estimations of isomer ratios for products of photonuclear reactions with multiple particle escape on antimony were performed using bremsstrahlung spectrum as projectile with end-point energies 74,9 and 85,7 MeV. Method of the induced activity measurement was applied. For acquisition of gamma spectra we used HPGe spectrometer with 20% relative efficiency. Linear accelerator of electrons LU-40 was a source of bremsstrahlung. Energy resolution of electron beam was about 1% and a mean electron current varied within (3.8 - 5.3)μA.

Detection of background thermal neutrons in a modified low-background germanium gamma-ray spectrometer

The paper presents the detection of background neutrons using the 558.4 keV gamma line emitted from excited 114Cd nuclei after neutron induced processes. Stable cadmium and 60 L water moderator were placed inside low background shield of high purity germanium (HPGe) based spectrometer. The method was applied to study diurnal mean variation of background neutron flux. For this purpose 1 h gamma background spectra of modified HPGe spectrometer were collected subsequently for 50.5 days and then summed in 24-h-cycle. Results for the 558.4 keV line are presented along with those of main background lines. The total gamma-ray spectrum was also analysed and results are presented and discussed. No cyclic structure was noticed for all examited lines but 2223 keV, for which some day-night effect is suggested to exist. Test of another moderator made of 108 kg of graphite was done, but the results obtained with water are more promising.

Simple, Immediate and Calibration-Free Cyclotron Proton Beam Energy Determination Using Commercial Targets

This work presents a simple method for determining the energy of the proton beam in biomedical cyclotrons, using no additional experimental set-up and only materials from radioisotope routine productions that are therefore available on-site. The developed method requires neither absolute efficiency calibration nor beam current measurements, thus avoiding two major sources of uncertainty. Two stacks composed of natural titanium thin foils, separated by an energy degrader of niobium, were mounted in a commercial target and irradiated. The resulting activities of 48V were assessed by a HPGe spectrometer.

The Evaluation of Brunei Bay Sediment Cores Sedimentation Rate Using 210Pb Radiometric Dating Technique

The use of radioisotopes 210Pb and 226Ra in establishing the geochronology of pollutants in the sediment core and sediment dating is being widely used in the world. The present study was conducted in Brunei Bay region of Malaysian waters to define the sedimentation rate and sediment age as well as to investigate the possible sources of pollutants into this bay. Sediment core samples were cut by layers, dried and analyzed using High Purity Germanium (HPGe) Spectrometer. Results obtained marked the time interval of 1875, 1956, 1962 and 1945 for sediment core B5, B9, B13 and LB consecutively. Sediment core of B9 and LB showed higher sedimentation rate compared to B5 and B13 due to the rapid development of urban and industrial. The increasing of sedimentation rate over the last 25 years was in line with the increasing of human activities surround the bay. Additionally, the health and distribution of mangroves surround Brunei Bay were important to determine the sediment movement which will affect the sedimentation rate in the bay. Overall, by controlling human activities as well as sustaining the mangroves population, could maintain and preserve the natural and unique environment of Brunei Bay.